Transcript Document 7127692

Organic Matter
The key to healthy soils
Fred Magdoff
Dept. of Plant & Soil Science
University of Vermont
Are these
problems or
symptoms?
compact soil
low nutrient levels
droughty
many pest problems
erosion and runoff
Symptoms
Problem
compact soil
Degraded and
unhealthy soil
low nutrient levels
droughty
many pest problems
erosion and runoff
Why are soils which in our
father’s hands were
productive now relatively
impoverished?
The depletion of the soil
humus supply is apt to be
a fundamental cause of
lowered crop yields.
—J.H. Hills, C.H. Jones, and C.
Cutler, 1908
Soil organic matter and
its management are at
the heart of soil health
Characteristics
of Healthy Soils
 Sufficient (but not excess) nutrients
 Good tilth
 Sufficient depth
 Good water storage and drainage
 Free of chemicals that might harm
plants
Characteristics
of Healthy Soils
 Low populations of plant disease and
parasitic organisms
 High populations of organisms that
help plant growth
 Low weed pressure
 Resistance to being degraded
 Resilience
Sustainable
Agriculture
Healthy Plants
Healthy Soils
Soil Organic Matter
There are three general
“types” of organic matter in soils
 Living
 Dead
 Very Dead
bacteria
plant roots
nematodes
fungi
—Living —
earthworms
mites
moles
springtails
amoeba.mov
fungi competition.mov
nematode&fungi.mov
small arthropods.mov
Root growth.mov
Root hair growth.mov
Soil ecology in balance
Tighter system
More fluid / greater biological diversity
•Low disturbance
•Crop rotation
•Direct seeding
•Build organic matter
•Permanent planting
•Infiltration
•Cover cropping
•Drainage
•Irrigation
management
•Soil fertility / slow
nutrient release
•Manure / biosolids
•Neutral pH
•Moisture conservation
•Residue cover
MANAGEMENT PRACTICES INFLUENCE ECOLOGY
•High disturbance
•Tillage
•Burning
•Steam sterilization
•Fumigants
•Monoculture
•Herbicides
•Overgrazing
•Fungicides
•Insecticides
Changing ecology of system
Imbalance in species
Some groups increasing in number; some groups eliminated
—Dead —
Recently dead soil organisms and crop
residues provide the food (energy
and nutrients) for soil organisms to
live and function. Also called “active”
or “particulate” organic matter.
—Very Dead —
Well decomposed organic materials,
also called humus. Humus contains
very high amounts of negative
charge.
All three “types” of soil organic
matter play important roles in
helping produce high yields of
healthy crops.
Soil organic matter
Organic matter is 1-6%
of total soil mass
living
10-20%
humus active (dead)
(very dead) 10-20%
60-80%
Organic Matter Influences a Vast Number
of Important Soil Properties
For Example:
• Nutrient availability
• Aggregation (and infiltration and drainage)
• Water storage
• Diversity and activity of soil organisms
• Soil color
• Presence of growth stimulating compounds
• Important global cycles — carbon, nitrogen, and
water — are strongly influenced by soil organic
matter
Nutrient Availability
As organic matter is
decomposed nutrients
are transformed into
forms that are
available to plants.
From 50% to close to 100% of the CEC
is due to soil organic matter
Organic
matter level
20
16
7%
CEC due to
12
organic matter
(me/100g soil)
8
3%
4
0
4.5
1%
5.0
5.5
6.0
pH
6.5
7.0
Ca++ Ca++
- Ca++ - -- - + - K
Mg ++ -++
- Ca
a) cations
held on
humus
Figure 4.3
Ca++ Mg ++
- - -- K+
b) cations
held on
clay
particle
-
Zn ++
c) cations
held by
organic
chelate
Cation
Exchange
Capacity
Cation
nutrients
held on
negatively
charged organic matter and clay.
and chelation
Corn grown in nutrient
solution with (right)
and without (left)
humic acids.
Photo by R. Bartlett.
Soil Tilth
QuickTime™ and a
decompressor
are needed to see this picture.
infiltration
runoff
a) aggregated soil
b) soil crusts after
aggregates break down
Root heavily infected with mycorrhizal fungi
(note round spores at the end of some hyphae).
Photo by Sara Wright.
Sticky substance, glomalin, surrounding root
heavily infected with mycorrhizal fungi.
Photo by Sara Wright.
Sticky substance, glomalin, surrounding soil
aggregates. Photo by Sara Wright.
carbon dioxide (CO2)
(0.04% in the atmosphere)
respiration
in stems
and leaves
photosynthesis
root respiration
and soil organic
matter
decomposition
crop harvest
crop and
animal
residues
carbon in
soil
organic matter
erosion
The role of soil organic matter in the carbon cycle.
Losses of carbon from the field are indicated by yellow color around
the words describing the process.
Karen Hills, 2007
Add
organic
matter
Increased biological activity
(& diversity)
Reduced
soil-borne diseases,
parasitic nematodes
Aggregation
increased
Decomposition
Pore structure Humus and other Nutrients
improved
released
growth
Harmful
promoting
substances
Improved tilth substances
detoxified
and water storage
HEALTHY PLANTS
160
y = 82.3x - 54.9
Yield (Bu/A)
140
r2 = .78
120
100
80
60
40
20
.8
1
1.2 1.4
1.6 1.8 2.0
2.2 2.4
Soil organic matter (%)
Relationship of corn yield and soil organic matter at the
end of a long term cropping experiment
Two conditions are necessary to maintain an
adequate amount of organic matter in the
soil. These are, first, an adequate supply, and
second, avoidance of a too-rapid loss...
– Lyon and Fippin. 1909.
QuickTime™ and a
decompressor
are needed to see this picture.